1). Field of the Invention
This invention relates generally to a method of constructing a microelectronic assembly, and more specifically to an encapsulant mixture that is used to form a mold over a microelectronic die of the assembly.
2). Discussion of Related Art
Integrated circuits are usually manufactured on wafer substrates. Such a wafer substrate is then “singulated” or “diced” into individual dies, each die carrying a respective integrated circuit. Such a die is then usually mounted on a substrate. The substrate provides structural rigidity to the entire assembly and has conductive lines for transmitting signals to and from the integrated circuit. An encapsulant is then formed over the die to protect the die and further rigidify the entire assembly.
An encapsulant is usually formed by locating a mold piece over the microelectronic die and then injecting an encapsulant mixture into a space defined between surfaces of the mold piece and the microelectronic die. The mold piece is removed after the encapsulant mixture is cured.
Existing encapsulant mixtures make use of an epoxy resin and highly reactive catalysts, such as triphenyl phosphine. Latent curing catalysts typically rely upon the use of one or more bulky ligands that sterrically hinder the catalyst, thereby reducing activity at all temperatures. In order to overcome slower polymerization rates resulting from the use of such ligands, higher concentrations of the catalyst are required. Higher concentrations of catalyst increases cost. Higher concentrations of catalyst also increases the overall activity of the catalyst and thereby reduces the latent effect of the catalyst.